Audio decoders which generate excited signals from coded speech signals input in units of frames and generate decoded speech signals from these excited signals are known. Of these types of speech decoders, in those which are adapted to low bit rate speech CODECs, the excited signals are treated with emphasis processing such as pitch emphasis processing or formant emphasis processing in order to improve the subjective sound quality of the decoded speech.
However, when frame errors occur in succession, the noise components are emphasized by these emphasis processes, thereby increasing the distortion and lowering the subjective sound quality.